The two bodies want small- and medium-sized business, especially those that send more than 500 items a day, to take advantage of the full opening up of the market to competition and an end to Royal Mail's monopoly this January.
Postcomm chairman Nigel Stapleton said: "Opening the mail market to competition will create a more vibrant postal market in the UK. It will introduce choice to a market that has been a monopoly for 350 years."
He added: "Customers will win through greater choice and new operators can win by innovating and developing new services and the Royal Mail can continue to grow and thrive."
An up-to-date list of suppliers can be found on Postcomm's .
Since 2003, bulk mailers, who send more than 4,000 at one time, have been able to choose alternative providers to Royal Mail.
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